This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A206828 #5 Mar 30 2012 18:58:12
%S A206828 1,1,2,1,2,1,2,2,1,1,1,1,2,2,3,2,2,1,8,2,1,1,5,2,1,2,11,1,0,1,4,1,3,4,
%T A206828 1,2,1,1,8,1,15,1,2,12,1,1,5,2,3,0,1,3,3,3,1,0,1,1,2,1,1,0,5,2,23,1,4,
%U A206828 0,4,1,7,3,1,12,2,24,2,1,8,3,3,1,6,0,3,1,37,1,3,26,1,1,1,0,4
%N A206828 Number of solutions k of C(2k,k)=C(2n,n) (mod n), where 1<=k<n.
%C A206828 For a guide to related sequences, see A206588.
%e A206828 2 divides exactly two of the numbers 20-1, 20-2, 20-6, so that a(3)-2.
%t A206828 s[k_] := Binomial[2 k, k];
%t A206828 f[n_, k_] := If[Mod[s[n] - s[k], n] == 0, 1, 0];
%t A206828 t[n_] := Flatten[Table[f[n, k], {k, 1, n - 1}]]
%t A206828 a[n_] := Count[Flatten[t[n]], 1]
%t A206828 Table[a[n], {n, 2, 120}] (* A206828 *)
%Y A206828 Cf. A206588.
%K A206828 nonn
%O A206828 2,3
%A A206828 _Clark Kimberling_, Feb 15 2012